ipop2d: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/ipop2d - from package: uw-imap

You may install the required package with command yum install {package}

Error in other languages:
ipop2d: bevel nie gevind nie
ipop2d: comandă negăsită
ipop2d: comando não encontrado
ipop2d: commande introuvable
ipop2d: command not found
ipop2d: käsku ei ole
ipop2d: không tìm thấy lệnh
ipop2d: komanda nerasta
ipop2d: Kommando nicht gefunden.
ipop2d: kommandot finns inte
ipop2d: komut yok
ipop2d: nie znaleziono polecenia
ipop2d: níor aimsíodh an t-ordú
ipop2d: no se encontró la orden
ipop2d: no s'ha trobat l'ordre
ipop2d: opdracht niet gevonden
ipop2d: parancs nem található
ipop2d: perintah tidak ditemukan
ipop2d: príkaz nenájdený
ipop2d: příkaz nenalezen
ipop2d: команда не найдена
ipop2d: командата не е открита
ipop2d: 命令找不到
ipop2d: コマンドが見つかりません